الف)
$\frac{{2m}}{2} \ne \frac{3}{{ - 1}} \to m \ne - 3$
ب)
$A = \left[ {\begin{array}{*{20}{c}}
4 \\
2
\end{array}\,\,\,\,\begin{array}{*{20}{c}}
3 \\
{ - 1}
\end{array}} \right] \to \left| A \right| = - 10 \ne 0\,\,,\,\,{A^{ - 1}} = \frac{1}{{ - 10}}\left[ {\begin{array}{*{20}{c}}
{ - 1} \\
{ - 2}
\end{array}\,\,\,\,\,\begin{array}{*{20}{c}}
{ - 3} \\
4
\end{array}} \right]$
$\left[ {\begin{array}{*{20}{c}}
x \\
y
\end{array}} \right] = \frac{1}{{ - 10}}\left[ {\begin{array}{*{20}{c}}
{ - 1} \\
{ - 2}
\end{array}\,\,\,\,\begin{array}{*{20}{c}}
{ - 3} \\
4
\end{array}} \right]\left[ {\begin{array}{*{20}{c}}
1 \\
3
\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}
1 \\
{ - 1}
\end{array}} \right] \to \left\{ \begin{gathered}
x = 1 \hfill \\
y = - 1 \hfill \\
\end{gathered} \right.$